Low molecular weight ethylene-based polymers are used in formulations to make hot melt adhesives, and other types of adhesives. Many such polymers are produced with a constrained geometry type catalyst system at low temperatures (<135° C.). It is desirable to find new polymerizations and catalyst systems capable of making these low molecular weight polymers at elevated temperatures, to allow for increased reactor throughput, decreased heat input for solvent devolatilization, and decreased reactor fouling. With such high temperature polymerizations and catalysts systems, it is desirable to use equivalent or lower levels of hydrogen, as compared to the current incumbent constrained geometry catalyst systems, to reduce or prevent gas-out from occurring in either the reactor, the reactor feeds, or the post reactor heater(s).
Some conventional polymerizations and catalysts systems are described in the following references: WO 2007/136494, US 2011/0282018, U.S. Pat. No. 6,869,904, U.S. Pat. No. 7,060,848, U.S. Pat. No. 6,806,326, U.S. Pat. No. 5,453,410, and U.S. Pat. No. 5,189,192. However, the polymerization of ethylene, and the polymerization of ethylene with one or more alpha-olefins, by transition metal catalysts of the art, are generally known to produce relatively high molecular weight homopolymers and copolymers, at high polymerization temperatures and low levels of hydrogen. Frequently such polymers and copolymers exhibit molecular weights (e.g., Mw) greater than 100,000 g/mole, and in some embodiments greater than 500,000 g/mole. At these molecular weight levels, the rheological behavior of the polymer is undesirable, because the polymers do not flow as desired, and may crystallize from the polymerization solution. As discussed, there remains a need for new polymerizations and catalyst systems, capable of making low molecular weight homopolymers and copolymers at elevated temperatures, and low hydrogen levels. This need has been met by the following invention.